The present invention relates to a reversible multicolor recording medium for recording image or data, and a recording method using the same.
Recently, the necessity of a rewritable recording technique is strongly recognized from the viewpoint of protecting the global environment. In accordance with the progress of computer network techniques, communication techniques, OA machines, recording media, and memory media, paperless technology is being spread at the office and home.
Recording media onto which information can be recorded and erased reversibly utilizing heat, i.e., so-called reversible thermal recording media are one of display media as a substitute for printed materials, and, as a variety of prepaid cards, point cards, credit cards, and IC cards spread, the reversible thermal recording media have been practically used in the applications in which the balance or other recorded information is needed to be visible or readable, and further they are being brought into practical use in the applications of copying machine and printer.
The reversible thermal recording medium and a recording method using the same are described in, for example, patent documents 1 to 4 below. These are so-called low-molecular substance dispersion type recording media, that is, recording media containing an organic low-molecular weight substance dispersed in a resin matrix, and the light scattering on the media is changed by experiencing high-temperature conditions to change the recording layer to an opaque or transparent state. Therefore, these media have a drawback in that the contrast between an image formed portion and an image unformed portion is unsatisfactory, and therefore, only the media improved in the contract by providing a reflective layer under the recording layer have been put into practical use.
On the other hand, for example, patent documents 5 to 9 below disclose a leuco dye type recording medium, that is, a recording medium having a recording layer containing a leuco dye, which is an electron donating color-forming compound, and a develop/subtractive agent dispersed in a resin matrix, and a recording method using the same. In the medium and method, as the develop/subtractive agent, an amphoteric compound having an acidic group for developing a leuco dye and a basic group for decoloring the colored leuco dye, or a phenolic compound having long-chain alkyl is used. The recording medium and recording method utilize coloring of the leuco dye itself, and therefore, the contrast and recognizability are favorable, as compared to those of the low-molecular substance dispersion type recording medium, and they are recently being widely practically used.
In the conventional techniques disclosed in the above patent documents, only two colors, specifically, the color of the material for the matrix, i.e., color of the base and the color changed by heat can be displayed. However, in recent years, for improving the recognizability and appearance, there are increasing strong demands of multicolor image display and recording of various data with color identification.
For meeting the demands, a number of recording methods have been proposed in which the above-mentioned conventional technique is applied and multicolor image display is achieved.
Patent documents 10 to 12 below disclose a recording medium in which layers or particles having different colors are render visible or hidden by a low-molecular substance dispersion type recording layer to achieve multicolor display, and a recording method using the same. However, in the recording medium having such a structure, the recording layer cannot completely hide the colors of the underlying layers and the color of the matrix is visible, so that a high contrast cannot be obtained.
In patent documents 13 and 14 below, there is disclosure concerning reversible thermal multicolor recording media using a leuco dye, but these recording media have repeating units having different hues in the surface, and therefore the area ratio of the individual hues to the actually recorded portion is small. Thus, there is a problem in that the recorded image is very dark or low in contrast.
In patent documents 15 to 23 below, there is disclosure concerning reversible thermal multicolor recording media having a structure in which recording layers using leuco dyes having different coloring temperatures, decoloring temperatures, and cooling rates are formed so that they are separated and independent from one another.
However, the recording media have problems in that temperature control using a recording heat source, such as a thermal head, is difficult and a favorable contrast cannot be obtained, so that the occurrence of fogging cannot be avoided. Further, it is very difficult to control the recording of multicolor, i.e., three colors or more merely by changing the heating temperature using a thermal head or the like and/or the cooling rate after the heating.
On the other hand, in patent document 24 below, there is disclosure concerning a recording method using a reversible thermal multicolor recording medium having a structure in which recording layers using leuco dyes are formed so that they are separated and independent from one another, in which only an arbitrary recording layer is heated and colored by light-to-heat transformation using laser. In this method, only an arbitrary recording layer can be colored by the effect of the wavelength selectivity of the light-to-heat transforming layer, possibly solving the problem of fogging accompanying the conventional reversible multicolor recording media.
However, in the above patent documents, no studies have been made on the wavelength of laser absorption and the order of the stacked light-to-heat transforming layers, and not only can the recording medium not always be surely colored with only a desired color, but also the problem of fogging has not yet been solved.
Patent Document 1: Japanese Patent Application Publication No: Sho 54-119377;
Patent Document 2: Japanese Patent Application Publication No: Sho 55-154198;
Patent Document 3: Japanese Patent Application Publication No: Sho 63-39377;
Patent Document 4: Japanese Patent Application Publication No: Sho 63-41186;
Patent Document 5: Japanese Patent Application Publication No: Hei 2-188293;
Patent Document 6: Japanese Patent Application Publication No: Hei 2-188294;
Patent Document 7: Japanese Patent Application Publication No: Hei 5-124360;
Patent Document 8: Japanese Patent Application Publication No: Hei 7-108761;
Patent Document 9: Japanese Patent Application Publication No: Hei 7-188294;
Patent Document 10: Japanese Patent Application Publication No: Hei 5-62189;
Patent Document 11: Japanese Patent Application Publication No: Hei 8-80682;
Patent Document 12: Japanese Patent Application Publication No: 2000-198275;
Patent Document 13: Japanese Patent Application Publication No: Hei 8-58245;
Patent Document 14: Japanese Patent Application Publication No: 2000-25338;
Patent Document 15: Japanese Patent Application Publication No: Hei 6-305247;
Patent Document 16: Japanese Patent Application Publication No: Hei 6-328844;
Patent Document 17: Japanese Patent Application Publication No: Hei 6-79970;
Patent Document 18: Japanese Patent Application Publication No: Hei 8-164669;
Patent Document 19: Japanese Patent Application Publication No: Hei 8-300825;
Patent Document 20: Japanese Patent Application Publication No: Hei 9-52445;
Patent Document 21: Japanese Patent Application Publication No: Hei 11-138997;
Patent Document 22: Japanese Patent Application Publication No: 2001-162941;
Patent Document 23: Japanese Patent Application Publication No: 2002-59654; and
Patent Document 24: Japanese Patent Application Publication No: 2001-1645.
As mentioned above, there are strong demands on the multicolor thermal recording and studies are vigorously conducted, but a recording medium or recording method having satisfactory recording properties from a practical point of view has not yet been found.